Threave Castle was built by Archibald Douglas "the Grim" in the mid-1300's on an island in the River Dee. It is reached by a 10 minute walk from the car park and then a boat ride out to the island. It is only a shell now, but it is easy to visualize it as it was - a formidable defensive tower. It also has the first known example of artillery defenses to protect the base of the tower from cannon. These were added in 1455. After the Crown took control of Threave from the Douglases, a succession of keepers held it for the king. Among them was George Carruthers, 6th of Holmains.